1. Field of the Invention
The present invention relates to a disk apparatus for recording and reading information data on an optical disk, and a disk determination method employed therein. More particularly, the present invention relates to a disk apparatus that can detect a wobble signal with high precision and determine the type of optical disk.
2. Background Information
There are known various types of optical disks, which include the following types among other types: read-only CD-ROMs (Compact Disk-Read Only Memory), read-only DVD-ROMs (Digital Versatile Disk-Read Only Memory), one-time recordable CD-Rs (Compact Disk-Recordable), one-time recordable DVD-Rs (Digital Versatile Disk-Recordable), rewriteable CD-RWs (Compact Disk-ReWriteable), rewriteable DVD-RWs (Digital Versatile Disk ReWriteable). In this specification hereinafter, one-time recordable CD-Rs, one-time recordable DVD-Rs, rewriteable CD-RWs and rewriteable DVD-RWs are collectively referred to as “recordable optical disks,” while read-only CD-ROMs and read-only DVD-ROMs are collectively referred to as “read-only optical disks.”
Recordable optical disks differ from read-only optical disks in that groove tracks and land tracks are formed in advance on the recording surface of the recordable optical disk. A wobbled groove that wobbles at a predetermined frequency is formed on the edge of the groove tracks, such that the rotational speed of the optical disk can be controlled based on a wobble signal that is detected from the wobbling of the wobbled groove. Also, land pre-pits are formed in the land track, so that the addresses can be read from a recordable optical disk in which data has not been recorded or a rewriteable optical disk. Generally, data is read from an optical disk by reflecting a light beam on the surface of the optical disk, and detecting the reflected light beam with a light detector.
When an optical disk is loaded onto a disk apparatus, it must be determined whether the loaded optical disk is a read-only optical disk, a recordable optical disk, or a rewriteable optical disk. One known method for determining the type of optical disk is a method that determines the type of optical disk based on whether or not a wobble signal that changes periodically due to the wobbling is detected by the optical pickup when the optical disk is rotated.
However, when the light detector of an optical pickup is placed in an unbalanced manner in the radial direction of the optical disk, the signal level of the wobble signal falls below the noise level even if there is a wobble in the groove of the optical disk. As a result, the wobble signal cannot be detected accurately. It is generally extremely difficult to place every light detector in a balanced manner in the radial direction of the optical disk. Furthermore, the balance of the light detector may change overtime, particularly due to changes in the temperature. Therefore, even if a light detector is placed in a balanced manner initially, the balance may be lost overtime.
Japanese Patent Application Publication No. 2002-329337 discloses a structure in which a light beam is split into a primary beam and two secondary beams, the position of an objective lens of an optical pickup is adjusted in the radial direction of an optical disk so that a wobble signal and a land pre-pit signal detected by the optical pickup have their maximum amplitudes, while adjusting the objective lens such that the offset of the differential signal created from the light signals from reflected lights of a primary beam and secondary beams on an optical recording medium is zero.
In this arrangement, however, since each of the reflected lights of the primary beam and the two secondary beams reflected from the recording surface of the optical disk must be received, the wobble signals cannot be detected with high precision at a low cost.
In Japanese Patent Application Publication No. 7-326062, a light beam is split into a primary beam and two secondary beams, and the primary beam and the secondary beams of a light beam are focused on the recording surface of a disk-shaped recording medium. The primary beam and the secondary beams of the light beam that are reflected on the disk-shaped recording medium are received. The accurate wobble signals are detected by canceling the offset of the differential signal created from the received primary beam with the secondary beams.
In this arrangement also, since each of the reflected lights of the primary beam and the two secondary beams reflected from the recording surface of the optical disk must be received, the wobble signals cannot be detected with high precision at a low cost.
In Japanese Patent Application Publication No. 10-69640, a light beam is split into a primary beam and two secondary beams, and the wobbled signal is obtained accurately by performing a subtraction with the light signals of the primary beam received by each of the inner half and the outer half of the light receiving photodiode after performing a normalization operation to each of the light signals of the primary beam.
In this arrangement also, each of the reflected lights of the primary beam and the two secondary beams reflected from the recording surface of the optical disk must be received and the normalization operation must be performed on the received lights. Therefore, the wobble signals cannot be detected with high precision at a low cost.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for improved disk apparatus and disk type determination method that overcome the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.